不同石粉含量的机制砂混凝土高温后力学性能

以受火温度、石粉含量为变化参数,设计并制作了210个100 mm×100 mm×100 mm的机制砂混凝土立方体试件,对其进行高温后的物理力学性能试验,获取了试件的质量损失率以及抗压强度和劈裂抗拉强度,建立了机制砂混凝土高温后抗压强度和劈裂强度的劣化模型,同时结合X射线衍射和扫描电子显微镜等技术,揭示了高温后机制砂混凝土力学性能劣化的微观机理。基于最高受火温度和质量损失率,分别提出了高温后机制砂混凝土抗压强度和劈裂抗拉强度评估计算式。结果表明:随着温度的升高,机制砂混凝土试件的表面颜色从灰色变成红褐色,最后呈白色,高温作用使试件表面出现了温度裂缝及剥落现象; 试件的质量损失率随着石粉含量的增加而增大; 混凝土抗压强度和劈裂抗拉强度随着温度的升高显著减小; 随着石粉含量的增加,混凝土抗压强度和劈裂抗拉强度先增大后减小,当石粉含量(质量分数)为10%时,混凝土强度达到最大值; 基于试验结果建立的高温后机制砂混凝土抗压强度和劈裂抗拉强度的劣化模型拟合度较好; 混凝土中掺入适量的石粉能促进体系中钙钒石和氢氧化钙等水化产物数量,当经受700 ℃高温后,水泥水化物脱水分解使混凝土内部裂缝和孔隙增多。

Mechanical Properties of Manufactured Sand Concrete with Different Stone Powder Content After High Temperatures

Based on the parameters of temperature and stone powder content, 210 cube specimens(100 mm×100 mm×100 mm)of manufactured sand concrete(MSC)were designed. The physical and mechanical properties after high temperature were tested. The mass loss rate, compressive strength and splitting tensile strength of specimens were obtained. The degradation models of compressive strength and splitting tensile strength after high temperature of MSC were established. The micro-mechanism of mechanical properties deterioration of MSC after high temperature were investigated by X-ray diffraction(XRD)and scanning electron microscope(SEM). The evaluation formulas of compressive strength and splitting tensile strength of MSC after high temperature based on the maximum fire temperature and mass loss rate were put forward. The results indicate that with the increase of temperature, the surface color of MSC specimens change from gray to reddish brown, and finally to gray. Temperature crevice and spalling arise on the surface of the specimen under high temperature. The mass loss rate of the specimen increases significantly with the increase of stone powder content. The compressive strength and splitting tensile strength of concrete decrease with temperature rise. The compressive strength and splitting tensile strength of the MSC specimens firstly increase, then decrease when the stone powder content is increased, and the concrete strength goes for a maximum when the content of stone powder reaches 10%(mass fraction). The deterioration model of compressive strength and splitting tensile strength of MSC after high temperature based on the measured results has good fitting degree. The amount of hydration products of MSC such as ettringite and calcium hydroxide can be promoted by adding stone powder. The cement hydrate dehydrates and decomposes in MSC, which makes the internal cracks and pores of concrete increase after high temperature of 700 ℃.